77' XS360 Backfires at high rpms/top of 6th

C

ciaostupido

XS400 Member
Messages
14
Reaction score
0
Points
1
Location
Pluto
Hey so I recently got a tune up kit for my XS360 and its never ran better! Anyway, now that I'm actually able to push it I've been trying to max it out and see how far it can go. I've noticed at high rpms, around 6k and up if I'm in 5th or 6th gear the bike starts to backfire/pop/sputter the engine feels like its overheating and I get a power loss and I have to back off the throttle to maintain speed.

I figured i'm running a bit lean, my jetting is stock with 17.5 Idles and 135 Mains. The Air/Fuel screws were 2.5 turns out and as of today I upped them to 3/3.5 and it seems alot more responsive and at higher rpms it doesnt backfire As Much as before.

Would bumping up the main to a 142.5 help remedy this? Or should I focus on the needle height now? I've read somewhere that they were jetted a bit lean from the factory, so I'm going towards this as a solution but I wanted to hear what some of you with experience think. Thanks!
 
Have you synced the carbs with a manometer? The idle mix screws are for up to 1/4 throttle not top end. The xs360 carbs run very rich compared to the xs400 ones. I have a set on my stock 82 xs400 now and have them on an 80 also. 1 turn out on the mix screws, 17.5 pilots, 3 clip on the needles and 135 mains. If you bike is all stock this should be close to what would work if the bike is tuned right. How do your plugs look?
 
I would try to stay near stock as Chris mentioned. Make sure to rule out other causes. I have experienced similar symptoms at high rpms when my bike had a dying battery, bad coils another time, etc.

If nothing else has really changed except for the tune up (not sure what you did), I would make sure nothing is simply dead or dying on you.

Just be conservative with the jetting; it often is not needed unless your exhaust and intake setting are modified and even then the requirements are modest at best.

I would even say that a loss of power and stumbling (even with a few little pops) is more a sign of being too rich over lean. Being a little lean on the top end won't usually cause those kinds of symptoms.

Remember: if your bike is stock and your carb settings are stock what are the odds that the carb settings are wrong? Not very good in my opinion. If everything is set stock any richness or leanness should be so subtle there is really no way you'll even notice it. If you're having overt significant symptoms as you describe I am leaning towards something else being wrong.
 
Yeah but are you guys actually trying to push your bikes past 80mph at WOT or just chilling cursing around at 60? I'm talking full throttle top of 6th @ 6k rpms.

I'll mess with the needle setting and see if that helps. Its only a fine tuning carb issue. Everywhere else its fine/responds well. The Tune Up was exactly that, you know those OG NipponDenso points/condenser/plugs kit they sell on ebay? We installed that. It runs great on the ND plugs lol, seriously. The coils could be going, but they have a nice fat blue spark so I dont think its there. The carbs were synced last year.

Also when I went to check the plugs, I cant tell its somewhere inbetween 'Overheating' and 'Normal' according to the Clymers manual. Are they suppose to be like a 2 stroke where you want the plug to look a nice coffee light brown? tytytyty
 
Mine will do well over 80 mph and when it tops out it doesn't stumble or spit, it just can't beat the wind resistance.

Messing with the needle will not help; it only controls the mid range. You just specifically said the problem is at 6k rpm in top gear WOT. Only the main jet matters at that stage.

I would listen to us; we have a lot of experience with these bikes. It sounds like you don't really know what you are talking about.

The appearance of a blue "fat" spark is not an objective test for the coils. Check the repair manual for the proper way to test them.

Adjust your valves if you haven't already. Make sure your timing isn't screwed up, etc.
 
so are you thinking its a timing issue/coils are overheating or not outputting like they should?, Where would you start?

So everything i've done so far is:
Installed new points and the condenser. Re timed it to the specs in the Clymer manual. Tested with a volt meter to make sure its within range.
Ultrasonic cleaned the carbs and jets.
Adjusted the Air/Fuel screws to 2.5 turns out.
Installed the Nippon Denso Spark Plugs that came with the Tune Up Kit.
Checked the Valves, they're in spec.

Am I missing anything? Also, whats the deal with the spark plugs on a 4 stroke? am I still aiming for the coffee brown color on the plugs or am I just going for clean as long as its not carbon fouled looking plugs?
 
nope, same problem. the NGKs made it worse actually. With the ND plugs it ran fine. I guess you folks don't really know what you're talking about and don't know what to do beyond stock settings. Thats too bad I was hoping someone here might have more info and be willing to help. I'll just have the mess around with the jetting on my own then. I'll let you guys know how it works out! :D
 
Believe it or not, most here do know what they are talking about. We don't have crystal balls that tell us what's wrong with others bikes sight unseen. Usually when you trouble shoot, you go through a type of 'flow chart' that starts at one possible point and moves further down the list until the issue is solved. Without the bike in front of us, we can't help much other than guessing. And all of of have given you a few steps in the 'flow chart'.

The fact that it only does it in 5th or 6th, when it's under it heaviest load/working the hardest, almost assures me it's a spark problem. I'd see this every day when I used to work in an auto shop- misfires on the free way, doesn't misfire on city streets. Sure enough it was always bad plugs. Are you positive they are the right plugs? The right wires? If you are running resistor plugs you need non-resistor caps and if running non-resistor plugs you need resistor caps. I want to say its different between cdi and points bikes as well. Since you say you bought a tune up kit, you need to check to see what crap they through together. Don't assume they gave you the proper parts. Are you sure the plug wires are seated in the coil properly? In the plug cap properly? These somewhat trivial things can bite you in the ass, they always get overlooked.
 
Interesting that you have this problem only in 5 and 6th, 4th is ok? Perhaps try on some uphill road... if you get this problem in every gear at least it is consistent problem at higher rpm.

If this was consistent "high rpm" problem my guess would be that either your ignition advancing springs are too weak throwing ignition way too early at high rpms (can be checked with stroboscope); or that spring that is holding point against excentric is too weak making moving point "dancing" at high rpms; I would also suspect condencer and try replacing it.

If problem disappears AT THE SAME RPMs by closing the throttle - than I would suspect fuel starvation and look for the problem in the carbs... or fuel filter... of fuel line.

Just a few thought out loud...
 
lol @ wolfe_11b. really you've never heard of a motorcycle 'tune up kit' before?

11377702_1449454072023800_819706499_n.jpg


You should check it out, they're pretty dope for the bikes that still use points ign setups, and considering ND made pretty much all the electronics on the bikes to begin with lol. The points even come pregapped!

So anyway I decided to replace my exhaust gaskets because the ones that were in there are pretty old and sure enough the bike runs excellent now. Thanks for the info guys!
 
Oh I've heard of them, and have no use for them. Glad you figured out your problem, thanks for wasting our time.
 
Pre-gapped points? What the hell does that even mean?

I'm not really buying it that the problem was an exhaust gasket either, but it doesn't matter. Have fun!
 
Wow, I've never encountered such a huge level of elitism on a motorcycle forum before. You guys should all just get Harleys lol. Also @wolf_11b jajaja man you are a funny guy! Calling me the hipster for drinking cheap shitty beer when you're the one who rides a cafe rawrcer. Atleast I know better then to chop my perfectly stock bike up lol. Also how have you fucks never heard of point gap before? How the hell do u guys get your bikes to run if you don't set the point gap? Lol.

For a bunch of backyard mechanics you guys are pretty rad. Cya 'round! :bike::bike::bike:
 
You gap points after you install them on the bike. It is the only way to do this. Remember you came here to ask a simple question and we gave you simple answers. We see a lot of people come and go:laugh: Next time your bike does a confusing thing that you can't fix, take it to a local dealership and pay them to figure it out. Have a good day sir:)
 
I don't discourage learning or asking questions.

It's totally fine if you're not an expert. Everyone has to start somewhere, but you keep disregarding what we're saying, acting defensive, and acting like you already know everything when it is crystal clear--based on your comments--that you really don't.

More receptive + less defensive = good response. It's that simple.
 
Interesting that the Nippon Denso tuneup kit lists compatibility with the XS360C,D,2D AND XS400D,E,F,2F, even though the two are supposed to take different temperature spark plugs.

The Haynes manual lists Nippon Denso spark plugs for both bikes, the W20EP for your XS360 and the W22EP for the XS400 (or NGK BP6ES vs BP7ES)

Which ND plugs came in the kit? Running the wrong temp plug could easily cause problems.
 
Wowza, that escalated quickly. You heard it from the professional folks, we're a bunch of elitist douche bags.

But his/her problem was fixed so obviously the best way to get help on this forum is to insult everyone who tries to help and hope for the best! :bike::bike::bike:
 

Similar threads

J
Carb tuning advice
Replies
16
Views
2K
JamesDavies
J
sandmanred
Needle position question 78 XS400
Replies
19
Views
2K
amc49
A
P
XS360 idle issues
Replies
13
Views
3K
pollestevens
P
E
Bike dies below 3k
Replies
4
Views
691
xschris
X
X
'77 XS400D - Choppy Idle / Ticking noise
Replies
0
Views
867
XS_Nick
X
Back
Top